Well, actually it's only a matter of your immagination...
By now I have just the script downloadable from my site, but you can add much more. For example you could:
- Ask to send you a photo from the picamera (I already did this for myself), so you can check a room
- Get data from sensors like temperature, pressure, humidity and/or presence of people and let the rpi send them to your smartphone
- Connect some relays to the raspberry and tell it to turn on/off an appliance
- Running a cyclic task (like the one for checking for my smartphone connected to the lan) you can be informed about something happening, like someone knocking to your home or the home phone ringing
- If you do not have a fixed ip for your internet connection you can also ask rpi to send your the current address, so you can connect to a local webserver or just ssh the rpi
- You can ask to close the curtains if it's raining, if you have the right circuitry of course
- If your rpi is a robot controller, instead of a home one, you can ask the robot to move or do something even if you are on the other side of the world
These are just few examples of what can be done. It's just another way to communicate with your raspberry pi, so you just need to analyze the received message and execute whatever routine you wish.